1. Field of the Description
The present description relates, in general, to three dimensional (3D) image generation, 3D media, and 3D display devices and, more particularly, to systems and methods for producing 3D images or depth and space media illusions without requiring viewers to wear 3D glasses or the like, e.g., multiplanar display systems providing a 3D display to viewers rather than projecting stereoscopic images requiring a viewing technology such as particular 3D glasses to be seen by an observer.
2. Relevant Background
There is a continuous desire and need to provide new techniques that provide cost effective but eye-catching content with depth and dimension. For example, it is desirable to grab the attention of crowds in shopping malls, on busy streets, in amusement parks, and other crowded facilities such as airports and entertainment arenas. As discussed above, 3D imagery is one exciting way to appeal to viewers and hold their attention.
However, the use of 3D imagery has, in the past, been limited by a number of issues. Typically, 3D projection is used only in low light environments and is not particularly effective in applications where there is a significant amount of ambient light such as an outdoor venue during the daytime (e.g., an amusement park or athletic stadium in the morning or afternoon where conventional 3D video image projection cannot compete with sunlight). Further, 3D projection technologies generally require the viewer to wear special viewing glasses, which is often inconvenient for many applications and can significantly add to costs.
One way of providing 3D imagery without glasses has been through the use of dual layer displays as these devices provide a simple and effective technique for creating dimensional imagery. FIG. 1A illustrates, with a perspective view, one basic and exemplary implementation of a dual layer display 100 during operation to provide a dimensional display without requiring a viewer to wear 3D glasses or headgear. The display 100 is a stacked and spaced combination of front layer transparent LCD panel 110 and a back layer LCD monitor 120.
As shown in FIGS. 1A and 1B (with FIG. 1B being a top view when the stack is vertically arranged), the LCD panel 110 is operated to provide front (or upper plane) content 114 (e.g., a fish) while the LCD monitor 120 is concurrently operated to provide back (or lower plane) content 122, 124 (with content 122 being a dark background content and content 124 providing a lighter/brighter and contextual content (e.g., rocks at the bottom of a pond/aquarium)). The foreground content 114 and background content 122, 124 are physically separated in depth by the spacing between LCD panel 110 and LCD monitor 120. The resulting image stack 114, 122, 124 exhibits parallax and correct accommodation cues. Typical content includes planar foreground and planar background images or layered projections of a 3D object.
In the dual layer display 100, the transparent LCD panel 110 does not emit its own light. It acts, instead, as a programmable transparency or filter over the back LCD monitor 120. White pixels on the transparent monitor 110 are clear, black pixels are opaque, and gray pixels are semi-transparent (as are pixels of other colors). During use of the display 100, the front and back layers' images 114, 122, 124 combine visually in a multiplicative manner (e.g., color component-wise).
As a result, as can be seen in FIG. 1B, portions of the front layer content 114 that are over the black back layer content 122 are not visible to the viewer (or do not appear as part of the dimensional display/output). Likewise, color mixing between the content 114, 124 can cause portions of content 114 to disappear or not be visible (e.g., red portions of front layer content 114 are not apparent over green portions of back layer content 124). A further problem with dual layer display 100 is that with bright back layer content (portions of content 124) the front layer content 114 is dark, low contrast, and semi-transparent, e.g., back layer content 124 is visible through the front layer content 114, which is often undesirable as it may be desirable for content 114 to be opaque (viewer would not expect to see through a fish in water in the provided example).
In brief, the appearance of the front layer content is dependent upon the back layer's content in dual layer display. Further, the front layer content is view dependent because of parallax between the two layers. The content creator must, therefore, carefully compose the front and back layer content so that the images in these two layers of content do not visually interfere with each other (as was the case in FIGS. 1A and 1B). In more complex schemes, the content provided in front and back layers of the dual layer display visually interact intentionally to display an apparently smooth volumetric image rather than just basic planar objects on each layer. This additional gain is achieved, though, at the expense of field of view of the display and the need for careful alignment of the displays of the front and back layers. In some applications, this effect is desirable and worth such a tradeoff.
Some efforts have been made to try to make the objects in the front layer content of a dual layer display appear visible against dark back layer content (e.g., try to make content 114 visible over dark back content 122 in FIGS. 1A and 1B). For example, one technique is to place a white silhouette of the front layer content in the hack layer content (e.g., provide a white backdrop to the content 114 in the portions 122 and 124 in display 100). The white silhouette acts as a localized backlight for the front layer content, and this technique also makes the front layer content appear opaque because part of the background content (that had previously shown through the front content) is removed to provide the white silhouette. The front layer content depends, therefore, (and is not independent from) upon the back layer content for visibility, opacity, and occlusion in such dual layer display systems.
While providing some improvements over prior dual layer displays, when viewed off-axis, the white silhouette on the back layer is no longer aligned properly with the front layer content. As a result, the silhouette can be seen by the viewer and may appear as a white halo on one edge of the front layer content (e.g., a white layer outlining the colored fish in the example of FIGS. 1A and 1B) and a dark and semi-transparent halo on the opposite side (e.g., portions of the front layer content may not be semi-transparent as was the problem with prior dual layer displays).
When viewed even further off-axis or by other viewers (not aligned perfectly with the display stack), the back layer silhouette and front layer content may be severely misaligned due to parallax such that the silhouette not longer properly serves its function (e.g., as a local backlight that also provides opacity). The front layer content/image would again appear as a transparency over the non-silhouetted background content and the silhouette hole in the background content would be readily apparent to the viewer. Disocclusion of the background is not possible with such a dual layer display as the previously hidden content does not exist (e.g., content removed for white silhouette). For larger depth separations between front and back layers, perspective effects also affect the quality of the display output. Another issue with such displays is that the silhouette only aligns with the front layer content at certain viewing distances.
Another approach used for dimensional displays involves depth fused displays, which are a class of layered displays that visually blend the layers to present an image volume rather than a stack of planar images. To increase the apparent number of layers, depth-weighted blending may be used in depth fused displays. Virtual pixels can be placed at depths between the layers by splitting the virtual pixel's luminance between the front and back layers proportional to its depth. The front and back layer content visually combine additively when the depth fused display is operated, and the viewer will accommodate on the virtual layer. For slight off-axis viewing, there is generally correct parallax and disparity.
There are several ways to implement a depth fused display including use of beam-combined LCDs, multiple scrim projectors, and two or more layers of stacked liquid crystal cells. Many of these displays can be used as dual layer displays with stacked planar images, and only the content needs to be changed to display depth fused images. A depth fused display uses two (non-transparent) LCD monitors that are optically combined using a 45-degree half-silvered mirror (also known as a beam combiner). The reflection of one display in the mirror appears stacked and spaced in front of (or behind) the direct view of the other display. Each layer is emissive, and the layers visually combine additively (color component-wise) because they are combined by the half-mirror. White pixels of the reflected monitor are bright, black pixels are transparent, and gray pixels are semi-transparent (as are other-colored pixels).
Other depth fused displays use two scrims stacked and spaced apart, with two projectors projecting front and back layer content onto the appropriate scrim. The two layers also visually combined additively. Unfortunately, the front and back layers have content that is semi-transparent and low contrast. A compact version of a depth fused display may use a stacked and spaced combination of a front transparent LCD without a polarizer and a back LCD monitor without an analyzer. Depth fusion in such a display is the result of the additive combination of the polarization rotation angles between the two displays, which appears as if the luminances of the two layers are added. In another implementation, the display is composed of a transparent emissive layer (e.g., an edge lit scattering plastic) between the front transparent LCD panel and rear LCD monitor. The transparent emissive layer backlights the front transparent layer, which visually combines additively with the hack layer.
Depth fused displays provide some advantages in providing a dimensional display to viewers without the need for glasses, but the disadvantages have blocked widespread implementation or use. For example, depth fused displays tend to have small fields of view due to parallax creating too large a misalignment between the two layers. Increasing the number of layers increases the field of view but adds to cost and complexity. Depth fusion also fails when the two layers are too far apart as the viewer cannot properly fuse the content provided at the differing depths. This may even occur for smaller layer separations such as when the display is viewed from a viewing distance that is too small (e.g., the viewer inspects the display close up).
Another approach to providing dimensional content is to use multilayer displays that include multiple image planes, e.g., foreground, midground, and background planes. Typically, multilayer displays are operated to produce volumetric images of 3D objects by placing cross sections of the object at each layer. The use of multiple layers provides smoother looking objects (with or without depth-weighted blending) and a larger field of view for apparently opaque objects than dual layer displays. In one particular such display, the display includes a spaced stack of twenty liquid crystal shutter panels and a high speed projector. Each shutter panel is operated to be transparent and scattering in sequence with the appropriate image projected for that one scattering layer. This implementation may also use anti-aliasing, which is a form of depth-weighted blending, to smooth the transition between layers.
In an early attenuation multilayered display, a stack of transparencies was used with each providing a cross section (or small depth of field image) of an object so as to create a volumetric image. Modern attenuation multilayered displays use multilayered LCDs and optimally compute the attenuation of each display (e.g., treating each LCD as a programmable attenuator) via tomography (i.e., integrated attenuation along a light ray path through the volume) to produce the desired light field (e.g., multiview images) emitted by the display. Unlike depth-weighted blending, tomographic methods do not require depth maps to be computed. Similar to depth-weighted blending, though, the field of view in multilayer displays is limited. Some efforts have been made to overcome this problem by using a switching directional backlight to allow multiple tomographic projections to be displayed in sequence with each projection only visible from a limited view.
In some display systems, floating images are provided in layered displays. For example, a display system may use varifocal optics to relay real images of a high-speed, selectively backlit transparent monitor at different depths. Such a display exhibits correct accommodation and vergence cues of up to twenty-four floating layers that the user/viewer can interact with during operation of the display. Multiplanar images have also been created using such a varifocal-based display as well as 3D hulls of objects. For occlusion capability, the varifocal display's monitor may be replaced with a multiview integral display whose real image is optically scanned in depth.
Floating images may also be provided using an immaterial depth fused display to project images onto layered fog screens. The use of a non-solid screen allows the viewers/users to interact with both layers. Infrared (IR) cameras may be used to track a single user to ensure the layers are visually overlapping correctly as the user moves. Additionally, the designers of depth fused displays and attenuation multilayered displays have reported the ability to have layers float outside the stack of LCD layers. The latter method produces different images in different view zones to create a stereoscopic image of the floating layer. However, while providing interesting imagery, these floating layers are not composed of real focused/scattering points of light at different depths, and, hence, the displays likely do not have correctly coupled accommodation and vergence cues for a realizable number of view zones.
Additionally, in modern interactive applications, the display device is increasingly used as an input device, e.g., a touch screen, gestural interfaces, and the like. The dual layer display is undesirable in such applications because a user would likely want to interact with content on both layers. However, the back display is physically inaccessible to the viewer/user as the solid front screen prevents the user from touching the back screen.
Hence, there is a need for a display assembly or system that produces solid, high-contrast front layer content or images that is independent of the back layer content/images being concurrently displayed. The system/assembly preferably would have a wide field of view and be simultaneously viewable by multiple people or viewers. Further, the display system/assembly would preferably be capable of producing a floating, real-image front layer so that the user/viewer can interact with both layers of the displayed imagery/content. The floating front layer may be capable of occluding the back layer content, exhibit appropriate parallax between layers, and also provide natural accommodation cues to the viewer. Additionally, some implementations of the display system/assembly may include an ability to display smooth volumetric images, and the display system/assembly may be extensible to multiple layers (rather than only two layers) while maintaining the aforementioned desirable qualities.